Long-term changes in postnatal susceptibility to pilocarpine-induced seizures in rats exposed to gamma radiation at different stages of prenatal development

Altered functional connectivity and network excitability in a model of cortical dysplasia

Focal cortical dysplasias (FCDs) are malformations of cortical development that often result in medically refractory epilepsy, with a greater incidence in the pediatric population. The relationship between the disturbed cortical morphology and epileptogenic activity of FCDs remains unclear. We used the BCNU (carmustine 1-3-bis-chloroethyl-nitrosourea) animal model of cortical dysplasia to evaluate neuronal and laminar alterations and how these result in altered activity of intracortical networks in early life. We corroborated the previously reported morphological anomalies characteristic of the BCNU model, comprising slightly larger and rounder neurons and abnormal cortical lamination. Next, the neuronal activity of live cortical slices was evaluated through large field-of-view calcium imaging as well as the neuronal response to a stimulus that leads to cortical hyperexcitability (pilocarpine). Examination of the joint activity of neuronal calcium time series allowed us to identify intracortical communication patterns and their response to pilocarpine. The baseline power density distribution of neurons in the cortex of BCNU-treated animals was different from that of control animals, with the former showing no modulation after stimulus. Moreover, the intracortical communication pattern differed between the two groups, with cortexes from BCNU-treated animals displaying decreased inter-layer connectivity as compared to control animals. Our results indicate that the altered anatomical organization of the cortex of BCNU-treated rats translates into altered functional networks that respond abnormally to a hyperexcitable stimulus and highlight the role of network dysfunction in the pathophysiology of cortical dysplasia.

Structural changes in the neocortex as correlates of variations in EEG spectra and seizure susceptibility in rat brains with different degrees of dysplasia

Disturbances of the early stages of neurogenesis lead to irreversible changes in the structure of the mature brain and its functional impairment, including increased excitability, which may be the basis for drug‐resistant epilepsy. The range of possible clinical symptoms is as wide as the different stages of disturbed neurogenesis may be. In this study, we used a quadruple model of brain dysplasia by comparing structural and functional disorders in animals whose neurogenesis was disturbed with a single dose of 1 Gy of gamma rays at one of the four stages of neurogenesis, that is, on days 13, 15, 17, or 19 of prenatal development.

When reached adulthood, the prenatally irradiated rats received EEG teletransmitter implantation. Thereafter, pilocarpine was administered and significant differences in susceptibility to seizure behavioral symptoms were detected depending on the degree of brain dysplasia. Before, during, and after the seizures significant correlations were found between the density of parvalbumin‐immunopositive neurons located in the cerebral cortex and the intensity of behavioral seizure symptoms or increases in the power of particular EEG bands. Neurons expressing calretinin or NPY showed also dysplasia‐related increases without, however, correlations with parameters of seizure intensity. The results point to significant roles of parvalbumin‐expressing interneurons, and also to expression of NPY—an endogenous anticonvulsant and neuroprotectant reducing susceptibility to seizures and supporting neuronal survival.

Changes of EEG spectra in rat brains with different patterns of dysplasia in response to pilocarpine-induced seizures

Disorders of neurogenesis at early developmental stages lead to irreversible structural and functional impairments of the brain. As further their consequences, increases in brain excitability and the development of drug-resistant epilepsy can frequently be observed in clinical cases. Mechanisms underlying these phenomena can also be examined on animal models of brain dysplasia. This study was conducted on rats with four degrees of brain dysplasia following exposure to gamma radiation on days 13, 15, 17, or 19 of prenatal development. When reached adulthood, the rats received electroencephalographic (EEG) transmitter implantation. Thereafter, pilocarpine was administered, and significant differences in susceptibility to seizures were detected depending on the degree of brain dysplasia. Before, during, and after the seizures, EEG was recorded in free moving animals. Additionally, the intensity of seizure behavioral symptoms was assessed. Strong and moderate correlations were found between the intensity of seizure behavioral symptoms, the power of particular EEG bands, and volumes of dysplastic brains and their regions. The data drew particular attention to correlations between variations in EEG spectra and changes in the midbrain and pons volumes. The results point to possible significant roles of these regions in the observed changes of susceptibility to seizures. Consequently, the frequently used experimental model was considered here not only as representing cases of cortical dysplasia but also of generalized, diffuse dysplasia of the whole brain.

Neuroprotective effect of Wogonin on Rat's brain exposed to gamma irradiation

Wogonin (5,7-dihydroxy-8-methoxy flavone), an active component isolated from the root of Scutellaria baicalensis Georgi. Neurotoxic effects of γ irradiation have been established in humans and animals. The current study was designed to evaluate whether wogonin could restrain γ irradiation-induced neurotoxicity in rats and to explore the underlying mechanisms. Rats were divided into five groups, 10 rats each. Group 1 was orally administered distilled water and served as control. Group 2 received an oral daily dose of wogonin (30 mg/kg). Rats in group 3 were exposed to a whole-body single dose of γ-irradiation. Animals in group 4 received an oral daily dose of wogonin (30 mg/kg) for 15 days then exposed to a whole-body single dose of γ-irradiation. In group 5, rats were exposed to a whole-body single dose of γ-irradiation then were orally administered a daily dose of wogonin (30 mg/kg) for 15 days. There were significant increases in malondialdehyde (MDA), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and Interleukin 6 (IL-6) levels and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) mRNA and protein expression. Whereas significant decreases in reduced glutathione (GSH), superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) level as well as nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) mRNA and protein expression in the irradiated group when compared with the relevant control. The cerebral cortex of irradiated rats showed vacuolization and nuclear pyknosis in the neuronal cells and focal gliosis. Wogonin administration pre- or post-irradiation significantly ameliorated all these previous effects. Wogonin had antioxidant and anti-inflammatory effects and ameliorated the histopathological changes in the brain.

Review: Roles for astrocytes in epilepsy: insights from malformations of cortical development

Malformations of cortical development (MCDs), such as cortical dysplasia and tuberous sclerosis complex, are common causes of intractable epilepsy, especially in paediatric patients. Recently, mounting evidence points to a common pathology of these disorders. Hyperactivation of mammalian target of rapamycin (mTOR) has been proposed as a central mechanism in most, if not all, MCDs. The transition from mTOR hyperactivation and cellular abnormalities to large-scale functional changes and seizure is, however, not fully understood. In this article we set out to review currently available information regarding MCD pathology, focusing on glial cells - especially astrocytes - and their interactions with the brain vascular system. A large body of evidence points to these elements as potential targets in MCD. Here, we attempt to provide a review of this evidence and propose some hypotheses regarding the possible chain of events linking primary glial dysfunction and epilepsy. We focus on extracellular matrix remodelling, blood-brain barrier leakage and failure of astrocyte-dependent removal of extracellular debris. We posit that the failure of these systems results in a chronically pro-inflammatory environment, maintaining local astrocytes in a state of gliosis, with increased susceptibility to seizures as a consequence.

Volumetric response of the adult brain to seizures depends on the developmental stage when systemic inflammation was induced

Inflammation has detrimental influences on the developing brain including triggering the epileptogenesis. On the other hand, seizure episodes may induce inflammatory processes and further increase of brain excitability. The present study focuses on the problem whether transitory systemic inflammation during developmental period may have critical importance to functional and/or structural features of the adult brain. An inflammatory status was induced with lipopolysaccharide (LPS) in 6- or 30-day-old rats. Two-month-old rats which experienced the inflammation and untreated controls received injections of pilocarpine, and the intensity of their seizure behavior was rated during a 6-hour period. Three days thereafter, the animals were perfused; their brains were postfixed and subjected to magnetic resonance imaging (MRI) scans. Then, volumes of the brain and of its main regions were assessed. LPS injections alone performed at different developmental stages led to different changes in the volume of adult brain and also to different susceptibility to seizures induced in adulthood. Moreover, the LPS pretreatments modified different volumetric responses of the brain and of its regions to seizures. The responses showed strong inverse correlations with the intensity of seizures but exclusively in rats treated with LPS on postnatal day 30. It could be concluded that generalized inflammation elicited at developmental stages may have strong age-dependent effects on the adult brain regarding not only its susceptibility to action of a seizuregenic agent but also its volumetric reactivity to seizures.

Inflammation in the developing rat modulates astroglial reactivity to seizures in the mature brain

Astrocytes participate in neuronal development and excitability, and produce factors enhancing or suppressing inflammatory processes occurring due to neurodegenerative diseases, such as epilepsy. Seizures, in turn, trigger the release of inflammatory mediators, causing structural and functional changes in the brain. Therefore, it appears reasonable to determine whether generalized inflammation at developmental periods can affect astrocyte reactivity to epileptic seizures occurring in the adult brain. Lipopolysaccharide (LPS) was injected in 6- or 30-day-old rats (P6 or P30, respectively). At the age of 2 months, seizures were induced, and pilocarpine and morphological changes of astrocytes located within the hippocampal formation were assessed. Additionally, expression of glial fibrillary acidic protein (GFAP), glutamine synthetase (GS), aquaporin 4 (AQP4), and inwardly rectifying potassium channel Kir 4.1 (Kir4.1) was determined using Western blots. The animal group given LPS on P6 displayed maximal susceptibility to pilocarpine-induced seizures, significantly higher than the group that received LPS on P30. In the immunohistologically examined hippocampal formation, the GFAP-immunoreactive area was not affected by LPS alone. However, it was reduced following seizures in naïve controls but not in LPS-pretreated rats. Increases in the ramification of astrocytic processes were detected only in adult rats given LPS on P30, not on P6. Seizures abolished the effects. Following seizures, the process ramification showed no significant change in the two LPS-treated rat groups, whereas it was significantly reduced in the dentate gyrus of LPS-untreated controls. Glial fibrillary acidic protein (GFAP) expression showed no changes induced with LPS alone and rose slightly after seizures. AQP4 content was lower in rats given LPS on P6 and was seizure-resistant in the two LPS-treated groups, contrary to a decrease in untreated controls. GS expression was not affected by LPS treatments and was reduced after seizures without an intergroup difference. Kir4.1 underwent highly significant increases in all groups experiencing seizures, but LPS alone had no effect. It can be concluded that the generalized inflammatory status led to some important changes in astrocytes reflected, in part at least by permanent modifications of their morphology and molecular profile. Moreover, the previously experienced inflammation prevented the cells from much stronger changes in response to seizures observed in adult untreated controls. The obtained results point to a link between the activation of astrocytes by transient systemic inflammation occurring during the developmental period and their subsequent reactivity to seizures, which may play an important role in the functional features of the brain, including its susceptibility to seizures.

Prenatal irradiation-induced brain neuropathology and cognitive impairment

Embryo/fetus is much more radiosensitive than neonatal and adult human being. The main potential effects of pre-natal radiation exposure on the human brain include growth retardation, small head/brain size, mental retardation, neocortical ectopias, callosal agenesis and brain tumor which may result in a lifetime poor quality of life. The patterns of prenatal radiation-induced effects are dependent not only on the stages of fetal development, the sensitivity of tissues and organs, but also on radiation sources, doses, dose rates. With the increased use of low dose radiation for diagnostic or radiotherapeutic purposes in recent years, combined with postnatal negative health effect after prenatal radiation exposure to fallout of Chernobyl nuclear power plant accident, the great anxiety and unnecessary termination of pregnancies after the nuclear disaster, there is a growing concern about the health effect of radiological examinations or therapies in pregnant women. In this paper, we reviewed current research progresses on pre-natal ionizing irradiation-induced abnormal brain structure changes. Subsequent postnatal neuropsychological and neurological diseases were provided. Relationship between irradiation and brain aging was briefly mentioned. The relevant molecular mechanisms were also discussed. Future research directions were proposed at the end of this paper. With limited human data available, we hoped that systematical review of animal data could relight research interests on prenatal low dose/dose rate irradiation-induced brain microanatomical changes and subsequent neurological and neuropsychological disorders.

Genetic animal models of malformations of cortical development and epilepsy

Malformations of cortical development constitute a variety of pathological brain abnormalities that commonly cause severe, medically-refractory epilepsy, including focal lesions, such as focal cortical dysplasia, heterotopias, and tubers of tuberous sclerosis complex, and diffuse malformations, such as lissencephaly. Although some cortical malformations result from environmental insults during cortical development in utero, genetic factors are increasingly recognized as primary pathogenic factors across the entire spectrum of malformations. Genes implicated in causing different cortical malformations are involved in a variety of physiological functions, but many are focused on regulation of cell proliferation, differentiation, and neuronal migration. Advances in molecular genetic methods have allowed the engineering of increasingly sophisticated animal models of cortical malformations and associated epilepsy. These animal models have identified some common mechanistic themes shared by a number of different cortical malformations, but also revealed the diversity and complexity of cellular and molecular mechanisms that lead to the development of the pathological lesions and resulting epileptogenesis.

The biochemical changes in hippocampal formation occurring in normal and seizure experiencing rats as a result of a ketogenic diet

In this study, ketogenic diet-induced biochemical changes occurring in normal and epileptic hippocampal formations were compared.

Brain dysplasia evoked by gamma irradiation at different stages of prenatal development leads to different tonic and clonic seizure reactivity

Rats with brain dysplasia evoked by interruption of different stages of prenatal neurogenesis show characteristic variations in susceptibility to seizures depending on the neurochemical specificity of pharmacological agents used to evoke seizures. To verify a discrepancy between the data obtained using different pharmacological models, neurochemically neutral electroshocks were applied here. To produce brain dysplasia of different degrees, pregnant Wistar rats were exposed to a single 1.0Gy dose of gamma rays on gestation days 13, 15, 17 or 19. From the postnatal day 60, their male offspring (E13s, E15s, E17s and E19s, respectively) were subjected to 21 daily electrical stimulations to evoke seizures. Profiles of tonic and clonic reactivity to electrical stimulation significantly differed from those observed following pilocarpine or kainic acid administration. E17s showed minimal intensity of tonic but maximal of clonic responses. On the contrary, very high tonic and low clonic reactivity was observed in E13s and E15s. Periventricular nodular heterotopias (PNHs) were observed exclusively in E15s and E17s. Generally, the size of PNHs was correlated positively with susceptibility to tonic seizures but negatively with susceptibility to clonic seizures. Analogous correlations with the size of the neocortex were opposite. E13s and E19s had brains devoid PNHs but showed high tonic seizure susceptibility similar to that in E15s. It can therefore be concluded that PNHs modified the type of seizure reactivity from tonic to clonic, depending of their size, but the presence of PNHs was not necessary for the development of seizure susceptibility itself.

Differences in the hippocampal frequency of creatine inclusions between the acute and latent phases of pilocarpine model defined using synchrotron radiation-based FTIR microspectroscopy

Temporal lobe epilepsy (TLE) is the most common type of epilepsy in adults. Of the animal models developed to investigate the pathogenesis of TLE, the one with pilocarpine-induced seizures is most often used. After pilocarpine administration in animals, three distinct periods--acute, latent, and chronic--can be distinguished according to their behavior. The present paper is the continuation of our previous study which has shown an increased occurrence of creatine inclusions in rat hippocampal formations from the acute phase of pilocarpine-induced status epilepticus (SE) and positive correlation between their quantity and the total time of seizure activity within the observation period. In this paper, we tried to verify if anomalies in hippocampal creatine accumulation were the temporary or permanent effect of pilocarpine-evoked seizures. To realize this purpose, male Wistar rats in the latent phase (3 days after pilocarpine administration) were examined. The results obtained for the period when stabilization of animal behavior and EEG occurs were afterwards compared with ones obtained for the acute phase of pilocarpine-induced SE and for naive controls. To investigate the frequency of creatine inclusions within the hippocampal formation as well as in its selected areas (sectors 1-3 of Ammon's horn (CA1-CA3), dentate gyrus (DG), and hilus of DG) and cellular layers (pyramidal, molecular, multiform, and granular cell layers), synchrotron radiation-based Fourier-transform infrared microspectroscopy was used. The applied technique, being a combination of light microscopy and infrared spectroscopy, allowed us to localize microscopic details in the analyzed samples and provided information concerning their chemical composition. Moreover, the use of a synchrotron source of IR radiation allowed us to carry out the research at the diffraction-limited spatial resolution which, because of the typical size of creatine inclusions (from a few to dozens of micrometers), was necessary for our study. The comparison of epileptic animals in the latent phase with controls showed statistically significant increase in the number of creatine inclusions for most of the analyzed hippocampal regions, all examined cellular layers, as well as the whole hippocampal formation. Moreover, for the hilus of the DG and CA3 area, the number of creatine deposits was higher in the latent than in the acute phase after pilocarpine injection. In light of the obtained results, an anomaly in the hippocampal accumulation of creatine is the long-term effect of pilocarpine-evoked seizures, and the intensity of this phenomenon may increase with time passing from the primary injury.

Magnetic resonance imaging--insights into brain injury and outcomes in premature infants

Preterm birth is a major public-health issue because of its increasing incidence combined with the frequent occurrence of subsequent behavioral, neurological, and psychiatric challenges faced by surviving infants. Approximately 10-15% of very preterm children (born<30 weeks gestational age) develop cerebral palsy, and 30-60% of them experience cognitive impairments. These adverse outcomes are related to a confluence of abnormal brain development along with white (WM) and gray matter (GM) injury sustained during the neonatal period. It is becoming apparent that the extra-uterine environment during this critical period (24-40 weeks gestation) in brain development has a profound and long lasting impact on the premature infant. Magnetic resonance imaging in the neonatal period and infancy provides a non-invasive, "in vivo" assessment of brain development and extent of brain injury. This not only helps understand the extent and timing of injury but also identifies infants who may benefit from early intervention to minimize the impact of the injury.

LEARNING OUTCOMES

Readers will be able to (1) appreciate the diverse impact of prematurity on neurodevelopmental outcome, (2) recognize the biological vulnerability of the developing brain in premature infants born between 24 and 40 weeks of gestation, (3) understand the role of magnetic resonance imaging (MRI) as a tool to detect abnormal development and brain injury in premature infants, and (4) see the potential role for novel MR imaging methods as biomarkers for brain development and injury in premature infants.

Physical training decreases susceptibility to subsequent pilocarpine-induced seizures in the rat

Regular motor activity has many benefits for mental and physical condition but its implications for epilepsy are still controversial. In order to elucidate this problem, we have studied the effect of long-term physical activity on susceptibility to subsequent seizures. Male Wistar rats were subjected to repeated training sessions in a treadmill and swimming pool. Thereafter, seizures were induced by pilocarpine injections in trained and non-trained control groups. During the acute period of status epilepticus, we measured: (1) the latency of the first motor sign, (2) the intensity of seizures, (3) the time when it occurred within the 6-h observation period, and (4) the time when the acute period ended. All these behavioral parameters showed statistically significant changes suggesting that regular physical exercises decrease susceptibility to subsequently induced seizures and ameliorate the course of experimentally induced status epilepticus.

Irradiation exacerbates cortical cytopathology in the Eker rat model of tuberous sclerosis complex, but does not induce hyperexcitability

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder characterized by multi-organ pathologies. Most TSC patients exhibit seizures, usually starting in early childhood. The neuropathological hallmarks of the disease - cortical tubers, containing cytopathological neuronal and glial cell types - appear to be the source of seizure initiation. However, the contribution of these aberrant cell populations to TSC-associated epilepsies is not fully understood. To gain further insight, investigators have attempted to generate animal models with TSC-like brain abnormalities. In the current study, we focused on the Eker rat, in which there is a spontaneous mutation of the TSC2 gene (TSC2+/-). We attempted to exacerbate TSC-like brain pathologies with a "second-hit" strategy - exposing young pups to ionizing irradiation of different intensities, and at different developmental timepoints (between E18 and P6). We found that the frequency of occurrence of dysmorphic neurons and giant astrocytes was strongly dependent on irradiation dose, and weakly dependent on timing of irradiation in Eker rats, but not in irradiated normal controls. The frequency of TSC-like pathology was progressive; there were many more abnormal cells at 3 months compared to 1 month post-irradiation. Measures of seizure propensity (flurothyl seizure latency) and brain excitability (paired-pulse and post-tetanic stimulation studies in vitro), however, showed no functional changes associated with the appearance of TSC-like cellular abnormalities in irradiated Eker rats.

Brains with different degrees of dysplasia show different patterns of neurodegenerative changes following pilocarpine-induced seizures. Histologic evidence of tissue damage correlated with MRI data

OBJECTIVE

Brain dysplasias produced by irradiation with gamma rays at various stages of prenatal development cause different post-natal susceptibility to seizures. To detect possible determinants of this difference, patterns of degenerative changes in the dysplastic brains following pilocarpine-induced epilepsy were analysed.

METHODS

Pregnant Wistar rats were exposed to a 1.0 Gy dose of gamma rays on gestation days 15 (E15) or 17 (E17). On post-natal day 60, their offspring received pilocarpine injections to evoke status epilepticus. Motor manifestations of seizure activity were observed continuously for 6 hours and rated. Six days following the status epilepticus, the rats were anesthetized and T(2)-weighted magnetic resonance (MR) images were obtained. Frontal sections of the brains were immunostained for immunoglobulins G (IgGs) to detect blood-brain barrier damage and IgG cell uptake and glial fibrillary acidic protein (GFAP) or S-100-beta protein to visualize astrocytes. Bandeiraea simplicifolia isolectin-B4 (BSI-B4) isolectin histochemistry was also performed to detect microglia/macrophages.

RESULTS

Tissue damages within epileptic brains as observed by light microscopy generally reflected changes in magnetic resonance imaging (MRI) at similar locations. Brains of rats irradiated on E15 or E17 and showing epileptic symptoms at comparable intensity also displayed different distribution of the pathologic changes. Among other post-epileptic changes, in rats irradiated on E17 as well as controls, the laterodorsal and ventrolateral thalamic nuclei showed signs of severe degeneration. In rats irradiated on E15, the nuclei were free of such changes.

CONCLUSIONS

The obtained data point to important differences in the pattern of propagation of epileptic activity in the dysplastic brains suffering from neuronal loss in functionally different structures.

Systemic prenatal insults disrupt telencephalon development: implications for potential interventions

Infants born prematurely are prone to chronic neurologic deficits including cerebral palsy, epilepsy, cognitive delay, behavioral problems, and neurosensory impairments. In affected children, imaging and neuropathological findings demonstrate significant damage to white matter. The extent of cortical damage has been less obvious. Advances in the understanding of telencephalon development provide insights into how systemic intrauterine insults affect the developing white matter, subplate, and cortex, and lead to multiple neurologic impairments. In addition to white matter oligodendrocytes and axons, other elements at risk for perinatal brain injury include subplate neurons, GABAergic neurons migrating through white matter and subplate, and afferents of maturing neurotransmitter systems. Common insults including hypoxia-ischemia and infection often affect the developing brain differently than the mature brain, and insults precipitate a cascade of damage to multiple neural lineages. Insights from development can identify potential targets for therapies to repair the damaged neonatal brain before it has matured.

Congenital brain dysplasias of different genesis can differently affect susceptibility to pilocarpine- or kainic acid-induced seizures in the rat

Interruption of neurogenesis and/or neuronal migration produces brain dysplasia modifying susceptibility to epileptic seizures in adulthood. The course of neurogenesis has a strictly defined time-table. Consequently, the developmental stage at which the interruption occurs determines what functional subsystem potentially involved in epileptogenesis will suffer from irreversible neuronal deficit. The present study attempts to verify a hypothesis that brain dysplasias of different genesis should also lead to different susceptibility to seizures evoked by receptor agonists of different functional specificity, like kainic acid or pilocarpine, a cholinergic or glutaminergic agonist, respectively. Pregnant Wistar rats were exposed to gamma-rays on gestation days 13, 15, 17 or 19 (E13, E15, E17 or E19). Sixty-day-old offsprings of the females were injected with kainic acid or pilocarpine to evoke status epilepticus. During a 6-h period following the injection, motor manifestations of seizure activity were recorded. Generally, the intensity of pilocarpine-induced symptoms was relatively low in rats irradiated on E13 or E15 but high in rats irradiated on E17 or E19. In rats treated with kainic acid, the trend was opposite, viz. the later the prenatal irradiation was performed, the less intense epileptic symptoms were induced in adulthood. The data provide evidence that dysplasias acquired during prenatal development may significantly amplify or reduce the brain susceptibility to seizures. However, this relation depends not only on the developmental stage at which the dysplasias were produced but also on the functional specificity of epileptogenic stimuli used in the experimental model of epilepsy.

A strong epileptogenic effect of mechanical injury can be reduced in the dysplastic rat brain

An exposure of rats to gamma-radiation at different stages of prenatal development produces brain dysplasias of different degree displaying also different susceptibility to pilocarpine-induced seizures. Following irradiation on prenatal day 13 (E13), the susceptibility is minimal and significantly lower even in relation to non-irradiated rats [Setkowicz, Z., Janeczko, K., 2003. Long-term changes in susceptibility to pilocarpine-induced status epilepticus following neocortical injuries in the rat at different developmental stages. Epilepsy Res. 53, 216-224]. On the other hand, the rat brain injured on postnatal day 30 presents very high susceptibility to seizures in the same pilocarpine model of epilepsy [Setkowicz, Z., Kluk, K., Janeczko, K., 2003. Long-term changes in postnatal susceptibility to pilocarpine-induced seizures in rats exposed to gamma radiation at different stages of prenatal development. Epilepsia 44, 1267-1273]. It could, therefore, be hypothesised that the congenital brain dysplasia produced by irradiation on E13 would minimize the highly increased susceptibility to seizures observed in the injured brain. Wistar rats were exposed to gamma-rays on E13 and they received a mechanical brain injury on postnatal day 30 (P30). On postnatal day 60, pilocarpine was injected to evoke status epilepticus. During a 6-h period following the injection, motor manifestations of seizure activity were recorded and rated. Seven days after pilocarpine injection, the animals were sacrificed and their brains were fixed. Pilocarpine injections in non-irradiated rats with brains injured on P30 evoked seizures of very high intensity and extremely high mortality in relation to non-injured controls. This high susceptibility to seizures following the brain injury was considerably decreased in rats irradiated on E13. The data provide evidence that the brain dysplasia in the rat acquired at this stage of prenatal development can significantly reduce the increased susceptibility to seizures evoked by the postnatal brain injury.

Different effects of neuroprotectants FK-506 and cyclosporin A on susceptibility to pilocarpine-induced seizures in rats with brain injured at different developmental stages

Susceptibility of the injured brain to epileptic seizures depends on the developmental stage at which the injury had been inflicted (our previous paper published in Epilepsy Res. 53 (2003) 216-224). The present study was designed to examine whether neuroprotective agents applied following the injury can decrease the seizure susceptibility. In order to solve this problem, the left cerebral hemisphere was mechanically injured in 6- and 30-day-old Wistar rats. Neuroprotectants FK506 or Cyclosporin A (CsA) were injected 20 min and 24h following the injury. On postnatal day 60, all the animals received single i.p. pilocarpine injections to evoke epileptic seizures. During a 6h period following the injection, the animals were observed continuously and pilocarpine-induced symptoms were recorded and rated. The animals were sacrificed 7 days after pilocarpine injection. In rats injured on postnatal days 6 or 30 (P6 or P30, respectively) and injected with FK-506 after the injury, signs of amelioration in the course of epilepsy were observed. Generally, proportions of rats suffering from heavy seizures were lower and/or their survival periods were longer. Following treatment with CsA, proportions of rats displaying heavy seizures were greater. It was accompanied by extremely high mortality (in rats injured on P6) or a longer duration of seizures (in rats injured on P30). The results appear to point to age-dependent differences between the mechanisms of action of the two neuroprotectants.

Contralateral response of macrophages and astrocytes to injury in the cerebral hemisphere of 6‐day‐old rat following prenatal gamma irradiation

Wistar pregnant rats were exposed to a single 1.0 Gy dose of gamma rays on gestational days 13, 15, 17 or 19 (E13, E15, E17 and E19, respectively). When offsprings of the irradiated females became 6-day-old, they received a mechanical injury of the cerebral hemisphere. One or 2 days after the injury, [3H]thymidine was injected and the animals were perfused. Brain sections were processed for BSI-B4 isolectin histochemistry or immunohistochemistry for glial fibrillary acidic protein (GFAP) or S-100-beta protein and subjected to autoradiography to visualise proliferating and non-proliferating macrophages or proliferating astrocytes. Significant changes in the contralateral response to injury related to the day of prenatal irradiation could be detected. The response was minimal following irradiations performed on E15 and E17. At those stages of prenatal development, the majority of cortical neurons with interhemispheric connections were formed. Therefore, irradiation-induced reduction of the neurons might minimise transfer of pathogenic stimuli to contralateral areas via degenerating nerve fibers. Consequently, the degree at which the contralateral glial response reflected reactive changes at the lesion site might also be minimal. Results of the present study do not show in detail mechanisms underlying the differences in the contralateral reactivity to injury. They, however, might be of importance to histopathological investigations using animal models of cerebral dysplasia.